High clouds and cirrus are starting to move back into the US Southwest in front of our next winter storm. The clouds were a problem all night in San Diego. Here in Tucson, the clouds only moved in at the very end of the night. Unfortunately, the forecast isn’t good for the Geminid maximum in southern CA or AZ.

From Bob Lunsford’s notes: “High clouds interfered with video observations last night. Only a small fraction of the activity seen on the 10th was recorded tonight. Unfortunately the weather forecast is not looking good. Lower clouds are expected to form tonight with mostly cloudy skies are expected right through the Geminid maximum.”

The Geminid rates continue to build as we approach its maximum this weekend. The Sigma Hydrids also continue to produce a consistent drizzle of activity.

After a few nights of rain, clouds, and fog, the weather has improved greatly in both Tucson and San Diego.

Bob had hist best night so far this year. From his notes: “The skies have cleared temporarily and despite the bright moon, an impressive number of meteors were recorded last night and this morning. The 120 total meteors recorded was the highest number obtained from home so far this year. Impressive numbers of Geminids (29), Antihelions (12), and Monocerotids (10) were recorded last night. The normally quite evening hours were also filled with activity. I wonder how many more meteors would have been recorded had there not been a bright moon? Hopefully the weather will remain favorable as close to the Geminid maximum as possible!”

The number of Geminids should continue to increase as they build towards their peak this weekend.

This weekend will see one of the year’s better meteor showers. In most years, the Geminids would rank as the year’s #1 or #2 best shower. Unfortunately, this year the Full Moon will put a damper on the show resulting in much lower rates.

From a dark, moon-less sky, the Geminids have been known to consistently produce rates of over 100 meteors per hour at their peak. Due to the bright Moon, the observed rate of Geminids will be much lower, probably in the 10-30 meteors per hour range. Still, if you are willing to brave the cold, the Geminids are one of the easier showers to observe. Unlike most showers that can only be observed in the early hours of the morning, the Geminids can be seen in good numbers as early as 10 pm and are great anytime after midnight. The Geminids will appear to radiate from the constellation of Gemini near the bright star Castor.

According to analysis of meteor video data by Sirko Molau, the Geminids are active for almost an entire month between the dates of November 23 and December 21. Though high rates are only possible within a few days of the peak. This year the peak is predicted for the nights of December 13/14.

Most meteor showers are produced by comets with orbits that extend out to the orbit of Jupiter or beyond. The Geminids are different. They are on a very short uncomet-like orbit that extends from a very close 0.14 AU from the Sun to a not so far 2.40 AU.

Orbits of (3200) Phaethon and the Geminids on 2008 December 14 UT. Orbit diagram produced with "C2A for Windows" (http://www.astrosurf.com/c2a).

In 1983, the parent body of the Geminids was discovered and surprisingly it looked like an asteroid. Since its discovery, the Geminid parent (3200) Phaethon has not shown any cometary activity. So what is it?

1) Phaethon could be a comet whose original orbit evolved into its current one after many millennia of close approaches with the inner planets. Some models of the formation of the Geminids require the shower particles to be released over many centuries to millennia. This is consistent with the behavior of a comet.

2) Phaethon may be a Main-Belt comet. Main-Belt comets are objects that originate in the outer Asteroid, or Main, Belt. Since they contain a sizable fraction of volatile material (water, carbon monoxide, etc.), they can occasionally exibit cometary activity. Four of these objects have been observed to display cometary activity in the Main Belt. Since they start on asteroid orbits, it is not too difficult for one of them to find itself on an orbit similar to Phaethon.

3) Phaethon is an asteroid that broke up in the past. There is evidence to suggest that Phaethon is just the largest piece of a past break-up. In fact, two additional asteroids that may once have been a part of Phaethon have been found, (155140) 2005 UD and 1999 YC. According to Peter Jennisken’s book “Meteor Showers and Their Parent Comets”, the Geminids can be explained by the break-up of Phaethon just after perihelion many orbits ago. Since Phaethon gets to within 0.14 AU (14% of the Earth-Sun distance), perhaps it split under the intense solar heat. BTW, this scenario does not rule out Phaethon as a ice-rich Main-Belt comet.

Clouds and rain spoiled the observing last night and tonight may bring more of the same. Conditions should improve by Tuesday evening. Unfortunately, it looks like the southwest US may be hit by a much stronger storm starting this weekend, just in time for the peak of the Geminids.

Clouds were again an issue for the first couple of hours of the night. With a storm forecast to move through AZ, tonight and tomorrow night may not be as productive.

The Sigma Hydrids (HYD) continue to put on a nice show with 5 of last night’s 34 meteors (15%) being from that shower. Though the there is video evidence that the Geminids (GEM) started a few weeks ago, last night marked the 1st night that the software I use was specifically looking for Geminids. (Any Geminids seen on previous nights would be flagged as Sporadics (SPO). When the data is analyzed in greater detail, the early Geminids will be identified.) A single Geminid was seen last night. By the end of next week, we will be seeing many more Geminids.

Last night was an experimental night. Since the start of my program to monitor meteors in Southern Arizona, I have been using a Supercircuits PC164C camera. This type of camera is usually used for video surveillance (i.e. watching parking lots at night, etc.) but it’s ability to detect work in low-light levels makes it good for astronomy.

Recently I purchased the latest version of this line of cameras, the Supercircuits PC164CEX-2. The manufacturers claim that it can detect objects 3 times as faint. One downside to the camera (with regards to meteor use) is that it has a higher resolution meaning smaller pixels. Since meteors are usually moving fast, smaller pixels result in the meteors spending less time on each pixel (called dwell time). Less time on each pixels means the meteor will appear fainter resulting in less meteors being detected.

So the verdict? Unfortunately, I’m not sure. On previous nights the PC164C was seeing 20-29 meteors per night. Last night the PC164CEX-2 caught 31 meteors. Since the camera wasn’t operating for the 1st ~5 hours of the night, it probably missed a few meteors. We’ll need to see how the numbers are on future nights.

The brightest meteor of the night (and perhaps ever detected by my camera) was a -5 fireball that appeared over Tucson at 2:51 am. Note, that compared to meteor videos from the older camera, the PC164CEX-2 produced video is much grainier.

Clouds were a problem for the 1st part of the night in Tucson, but after that the night turned out well. Clouds continue to be a problem in San Diego.

From Bob Lunsford’s notes: “Clouds continue to hamper my video observations. Tonight there were some breaks in the cirrus and cirrocumulus so I went ahead and ran the camera. The results were meager but better than nothing!”